1. Field of the Invention
This invention relates to a paper web threading apparatus for use in a rotary printing press as a paper web handling machine.
2. Description of the Prior Art
In paper web handling machines, many paper web threading apparatuses in which a paper web is threaded substantially along a web threading path through a paper web threading member movably arranged substantially in parallel with the paper web threading path are disclosed, for example, in Japanese Laid-Open Utility Model Publication No. SHO 62-925, Japanese Laid-open Patent Application No. SHO 61-167553, Japanese Laid-open utility Model Application No. SHO 63-163939 and No. HEI 2-29727, and Japanese Laid-open Patent Application No. HEI 2-86249, etc.
Each of the paper web threading apparatuses disclosed in the aforementioned publication is adapted for use in a rotary printing press, and constructed such that, in the rotary printing press including a paper web driving device comprised of a slitter for slitting a paper web in the longitudinal direction thereof into web strips and a drag roller for sending forwards the divided web strips towards the downstream side of a paper web threading path, the paper web is threaded through the intermediary of the paper web threading members substantially along the paper web threading path extending from a paper web supply station to the paper web dividing device, and then each of the divided paper webs obtained by the action of the dividing device is further threaded through the relevant paper web threading members substantially along the relevant paper web threading path leading to the following station.
Further, the paper web threading apparatus disclosed in Japanese Laid-open Patent Application No. SHO 61-167553 comprises, in addition to the above-mentioned configuration, a means for detecting slack of each of divided paper web strips on the downstream side of the paper web dividing device, the slack detector means each being connected with a driving means for each paper web threading member, the arrangement being made such that when the slack detector means detects any slack the operating speed of the driving means of the corresponding paper web threading member is increased to eliminate slack of the divided paper webs.
In the above-mentioned paper web threading apparatuses, the paper web threading members adapted to thread a paper web and each of divided web strips substantially along their respective paper web threading paths are driven by their respective driving means separate from a driving system of a rotary printing press which is a paper web handling machine.
Further, the divided web strips are threaded along their individual web threading paths, and the length, the number and degree of directional changes (or flexures) of the paths are different, and therefore there is a difference in loading to which the paper web threading numbers are subjected from the mechanism supporting them when they are moved substantially along their respective web threading paths.
Still further, transmission of the driving force by the driving means to the paper web threading members resorts to the frictional force exerted between the peripheral surface of rotating member of the driving means and the outer surface of the paper web threading member. This frictional force varies with changes in physical properties of the peripheral surface of the rotating member and the outer surface of the paper web threading members with the lapse of time and/or due to use thereof. Further, the frictional force also varies with other factors such as, for example, adhesion of extraneous matters to the peripheral surface of the rotating member and the surface of the paper web threading members. Therefore, it is rarely the case that the frictional forces exerted between the peripheral surfaces of the rotating members of the driving means and the surfaces of the paper web threading members in the respective web threading paths become equal in magnitude.
As a result of combination of the above-mentioned factors, when a paper web and each of divided paper webs are threaded by their respective paper web threading members along the relevant paper web threading paths, respectively, a variable difference occurs between the operating speed of the paper web handling machine when each of the paper webs is threaded along its path (or the paper web delivery speed of the web handling machine to the downstream side when each of the paper webs is threaded along its path) and the speed of movement of each of the paper web threading members. Further, a variable difference occurs also between the speeds of movement of the paper web threading members which serve to thread divided web strips along their relevant paths.
Yet further, in comparison of the length of the actual paper web threading path with the path along which the paper web threading member is moved, at a place where the adjusting roller is disposed and the length of the paper web threading path is variable, the length of the path along which the paper web threading member is moved is longer than the maximum length of the paper web threading path which is variable, so that the length of the path along which the paper web threading member is moved is slightly longer than that of the actual paper web threading path.
Consequently, the paper web and each of the divided paper webs to be threaded substantially along their respective web threaded paths slacken more than the amount required with the result that the paper web and the divided paper webs tend to shift to the left or to the right relative to the direction of threading of paper webs, interfere with the mechanism adjacent to the relevant paper web threading path or hang down to a large extent, or the leading portion and the trailing portion of each of the paper web and the divided paper webs tend to interfere with each other, and as a result, each of the paper webs being folded partially, thus causing unbalance in tension exerted on the paper web and the divided paper webs, respectively, resulting in tear of the paper webs.
Further, the paper web threading apparatus disclosed in Japanese Laid-open Patent Application No. SHO 61-167553 comprises a means for detecting slack of divided paper webs for concentrating the slack to one place and restraining it below a predetermined amount, and a means for increasing the speed of movement of the paper web threading member to eliminate the detected slack. However, the arrangement for concentrating such slack to one place tends to impair the working environment due to air blow, that is, it causes suspension of dust such as paper scraps, etc. and generation of noise, thus giving operators physical and/or mental pain. On the other hand, arrangements for concentrating slack of paper webs to one place by means of a common roller type web tensioner require provision of a comparatively large space for installing the roller type web tensioner in the web threading path. However, at places in the vicinity of the paper web dividing device or near the adjusting rollers where each of divided paper webs is liable to slacken to a comparatively large degree, guide rollers and turning bars are normally concentrated, thereby rendering it difficult to provide the space for installing the web tensioner.